1. Field of the Invention
Polypyrrolidone (nylon-4) can be spun into fiber having useful properties. The polymer is produced by the alkaline-catalyzed polymerization of 2-pyrrolidone (see U.S. Pat. No. 3,721,652) and is spun into filament by extrusion from multi-hole spinnerets. Melt spinning is accomplished by extruding the polymer in a molten condition, but at melt temperatures the polymer tends to degrade and revert to monomer. Several other spinning processes are at least hypothetically applicable to polypyrrolidone spinning, but they depend on the extrusion of a polymer solution. In dry spinning, a solution of polymer is extruded into a heated zone in which the solvent evaporates and from which the filaments are collected. In wet spinning, a solution of polymer is extruded into a liquid bath in which the solvent is at least partially removed from the filament and from which the filaments are collected. Wet spinning is carried out at much lower temperatures than melt spinning and, normally, at substantially lower temperatures than dry spinning. In the little used process of gap spinning, a solution of the polymer containing a volatile diluent is extruded into a heated zone. The volatile diluent evaporates in the "gap" between the spinneret and a liquid bath. Normally, substantial amounts of solvent and diluent are removed from the filament in the liquid bath and the filament is then collected. Dry, wet and gap spinning processes are herein referred to as "solution spinning."
2. Prior Art
Relevant articles on the spinning of fiber-forming polymers can be found in "Man-Made Fibers, Science and Technology", Volume 1, H. F. Mark et al. Ed., Interscience Publ., New York.
U.S. Pat. Nos. 2,711,398 and 3,060,141 disclose the spinning of polypyrrolidone from meta-cresol or formic acid solutions and aqueous formic acid solutions respectively. U.S. Pat. No. 2,734,043 teaches the dilution of fiber-forming formic acid solutions of polypyrrolidone with aliphatic and chloroaliphatic acids. U.S. Pat. Nos. 2,980,641, 3,003,984, 3,033,810 and 3,042,647 disclose wet spinning solutions of polypyrrolidone comprising phytic acid, trichlorinitropropanol, ferric chloride, and chlorinated phenol, respectively. U.S. Pat. Nos. 3,076,774 and 3,324,061 report the dry spinning of polypyrrolidone from aqueous solutions prepared from superheated water, 120.degree.-180.degree. C.